bison version is too old

[Peng Yu]

The bison that I installed by macports is too old. Could somebody
updated bison to the latest version?

$bison --version
bison (GNU Bison) 2.3
Written by Robert Corbett and Richard Stallman.

Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.